Although experiments with the microphone are of such recent date, they have been very various, and among other curious experiments we learn from the English newspapers that the attempt has been made to construct an instrument on the same principle as the telephone, which shall be sensitive to the variations of light. It is known that some substances, and particularly selenium, are electrically affected by light, that is, that their conductivity varies considerably with the greater or less amount of light which is shed upon them. If, therefore, a circuit in which a substance of this nature is inserted, is abruptly subjected to a somewhat intense light, the increase of resistance which results from it ought to produce a powerful sound in a telephone inserted in the circuit. This fact has been verified by experiment, and Mr. Willoughby Smith infers from it, as we have already suggested, that the effects produced in the microphone are due to variations of resistance in the circuit, which are produced by more or less close contacts between imperfect conductors. In order to obtain this effect under the most favourable conditions, Mr. Siemens employs two electrodes, consisting of network of very fine platinum wire, fitting into each other like two forks, of which the prongs are interlaced. These electrodes are inserted between two glass plates, and a drop of selenium, dropped in the centre of the two pieces of network, connects them on a circular surface large enough to establish sufficient conductivity in the circuit. It is on this flattened drop that the ray of light must be projected. APPLICATIONS OF THE MICROPHONE. The applications of the microphone increase in number every day, and in addition to those of which we have just spoken, there are others of really scientific and even of practical interest. Among the number is the use which can be made of it as a system of relays for telegraphy, in science for the study of vibrations imperceptible to our senses, in medicine and surgery, and even in manufactures. _Its application to Scientific Research._--We have seen that several physicists, including Messrs. Spottiswoode, Warwick, Rossetti, Canestrelli, Wiesendanger, Lloyd, Millar, Buchin, and Blyth, have been able to hear what is said in a telephone which has no iron diaphragm, but it was so difficult to establish the fact that it has been often disputed. More certain evidence was desirable, and the microphone is an opportune agent for affording it. The ‘Telegraphic Journal’ of September 1, 1878, observes that M. du Moncel, in order to claim the victory in his controversy with Colonel Navez, had still to show that the sounds which appeared to be inarticulate in telephones without a diaphragm might become intelligible if they were intensified. This has been done for him by the use of Mr. Hughes’s microphone, and the following experiments were made for the purpose.